Rock bolt anchored by explosive forming



p 1964 E}. w. PARSONS 3,148,577

ROCK BOLT ANCHORED BY EXPLOSIVE FORMING Filed Feb. 27, 1962 2 Sheets-Sheet l l fdfika h g MENTOR 50mm m mesa/vs ,9? I BY M ATTORNEY 1 lllllllu kll lllllllll Fl 3. 3B

INVENTOR Sept. 15, 1964 E. w. PARSONS ROCK BOLT ANCHORED BY EXPLOSIVE FORMING 2 Sheets-Sheet 2 Filed Feb. 27, 1962 F/GIJA rlazb FIGZZA EDWARD W. PARSONS United rates i atent nice 3,148,577 ROCK B0111 ANCHQRED BY EXPIXESIVE FURMHNG Edward W. Parsons, Spokane, Wash, assignor to the United tates of America as represented by the Secretary of the Interior Filed Feb. 27, 1%2, Ser. No. 176,15i 11) Claims. ('81. 8565) (Granted under Title 35, 11.5. Code {1952), see. 266} The invention herein described and claimed may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of royalties thereon or therefor.

This invention relates to improvements in rock bolts used in mining and construction operations as an aid in the support of rock around underground openings or surface rock exposures. Such bolts have particular utility for reinforcing rock formations by providing subsidiary support under sagging or weakened strata of these formations.

Previous to the time that rock bolts were introduced as a means to support underground openings, mine roofs were most often secured in place by means of timbers arranged as horizontal beams supported by posts. Placing the timbering in supporting position was usually a costly and time consuming operation, and the posts often took up much needed space. Noteworthy improvements in safety, convenience, and savings in time and expense, have resulted from the use of rock bolts for roof supports in mine passages. When applied for this purpose the bolts clamp the overhead rock layers together so that the strata in the roof structure is stabilized. These bolts have also found important utility in stabilizing steep rock slopes along highways and railroads.

A rock bolt is generally made effective to support a mine roof by having the bolt hold a relatively heavy plate in contact With the roof surface wherein the bolt is maintained in place by reason of the intimate contact of an outer surface thereof with the surface of a hole drilled up through the overhead rock in the mine roof. In the present invention, this intimate contact anchoring the rock bolt to the strata of the mine roof, is produced by the discharge of an explosive contained within the bolt. Prior art explosively actuated mine roof bolt anchors such as disclosed in Patents Nos. 2,573,880 and 2,618,192, issued November 6, 1951, and November 18, 1952, respectively, to Robert Temple, have holding capabilities which are limited by the construction characteristics of the means provided to accomplish the anchoring contact. The devices described in both patents rely upon split collet-like sleeve elements having relatively short gripping surfaces which are arranged to be deformed outwardly to contact the surface of a drilled hole by tapered stud expander elements projected by an explosive force to enter between the split elements. According to the present invention, the explosive force for the bolts makes available for intimate gripping contact with the surface of the drilled hole, a completely intact surface along a substantial length of the rock bolt.

It is therefore an object of the present invention to provide a conveniently installed rock bolt having an enlarged area of anchoring contact.

Another object of the present invention is to provide an explosively actuated rock bolt whose anchoring capabilities may be predetermined.

These and other objects and advantages of the invention will be more clearly understood from the following description of a preferred embodiment of the invention, considered together with the accompanying drawings wherein:

FIG. 1 is a perspective View of a rock bolt embodying the invention, with sections cut out to reveal the several parts of the internal arrangement of the rock bolt;

FIGS. 2a and 215 show rock bolts having different extents of expanded contacting area for anchoring the bolts; and

FIGS. 3a and 3b are schematic representations illustrating different arrangements of the explosive charges within the rock bolt, and the corresponding varying effects on the formation of expanded contacting areas.

Referring to FIG. 1, a preferred embodiment of the invention may be seen as comprising an elongated cylindrical hollow casing 10, having supported therein in concentric relationship therewith, an elongated cylindrical capsule 311, containing explosives made operative for purposes to be presently explained. The tubular body constituting casing 19, shown in open section in FIG. 1, and in more complete form in FIGS. 2a and 2]), may be made of a dead annealed, mild steel hydraulic tubing. Also as seen in these figures, the casing 10 is rigidly fixed to a solid bolt element 211. A suitable material for bolt 20, would be one-inch steel rod, although for other requirements the possible use of other sizes and materials for the bolt, is self-evident. Starting at one end 23 of the bolt and extending along an appropriate length thereof, is a screw thread 22, such length being about 4 to 6 inches for the one-inch rod. A short inclined passage in the body of the bolt extends between a small hole in the center of the face surface at end 24- of the bolt, and a imilar hole 25 in the cylindrical surface of the bolt. The connection joining the tubular casing 16 to the bolt 24), is facilitated by three sets of two small overlapping holes 11, drilled through the casing at equidistant points around the casing at a short distance from one end 12 thereof. When the bolt is inserted and snugly fitted Within the opening in casing end 12 such that its end 24 is past and slightly beyond holes 11, the bolt is in position to be secured by the welds 13 received in holes 11. To assure a suitably tight, strong and durable junction between the bolt and casing, there is applied here a continuous seam Weld 14, circumferentially around the bolt 26 As more clearly seen in FIGS. 2a and 2b, the rim of casing end 12 is thereby made integral with the bolt material. In position to block the opening in the other end 15 of the casing 18, is mounted a round steel plug 16 of substantial thickness. This plug is retained within the opening to have a very limited swivel action about a hard steel pin 17, passing therethrough, and supported in bearing holes through the casing wall, one of the holes being indicated in FIGS. la and 2:1, as an aperture 13. Plug 16 may swivel in this manner since the bearing holes 18 locate the longitudinal axis of pin 17 slightly offset from and parallel to a diametrical axis across the opening in casing 10, and at a short distance from the casing end 15, as shown in FIGS. 2a and 2.5. As will be hereinafter more fully explained, this offset prevents the pin from taking the full force of the shock of the explosion.

Capsule 311 at the hub of the arrangement shown in FIG. 1, may be seen as comprising a thin-walled tubular element 31, and a detonator device 35. A short tubular section 36, fitted over the detonator device 35, adapts the latter to be partly inserted into one end of a second and slightly longer tubular section 37. Tubular element 31 is received in the remaining part of the tubular section 37, whereby it is joined to the detonator device. This junction is additionally sealed to be waterproofed by the application thereto of a mastic or other similar waterproofing material. Within the tubular element 31, there is fitted securely in place the explosive material 39, such as PETN (pentaerythritetetranitrate), in a standard grade of Primacord. An approximate charge for use in connection with anchoring a one-inch bolt, would be a single strand of grains (per foot) Primacord, or multiple amass/7 are used, an additional 4 inch piece of the Primacord would be inserted at the detonator end of the capsule. Detonator 35 may be a No. 6 instantaneous cap with lead wires 40 longer than the total length of the rock bolt to which it is applied. A small amount of PETN powder is placed between the detonator and the Primacord to insure the necessary intimate contact to achieve the explosion. A suitable extension 41, of the tubular element 31, beyond the Primacord within the element, is filled with mastic to provide a waterproof seal at this end of the element, and is effective to prevent damage to the welds where the bolt and casing are joined which might result from the explosive action.

Around the cylindrical surface of capsule 30 are securely fitted two or more star-shaped washers 42, made of rubber or other similar material. The washers are suitably positioned at appropriate places along the capsule to permit the capsule to be properly supported within the casing 10, in its concentric relationship therewith, Prior to inserting the capsule 30 into the casing 10, the detonator lead wires 40 are pulled through a very small opening 44 in a disk-like rubber gasket 43, and placed into the casing such that the wires may be threaded into the center hole in the face of bolt end 24. After the wires 40 pass through the bolts inclined passage, they are received at hole in the bolt, and their extended ends brought outside the bolt. With the help of the extended lead wires 40, the capsule is pulled open end first, into the casing and centrally positioned therein by means of the star-shaped washers 42. Gasket 43, on the wires 40, is carried therewith to contact the face surface at bolt end 24, and to cover over the opening therein. As may be seen in FIG. 1, the detonator end of the capsule is arranged to face the outer or plugged end of the casing 10, whereby the opposite end of the capsule may be placed to firmly contact face 45 of the gasket 43. To complete the rock bolt assemblage, water or other suitable fluid is supplied to the casing 10 through the opening in its end 15, until all the space 47 between the capsule 30 and the casing 10 is completely filled with liquid when the casing is sealed. Substances such as gels, waxes, fats, paraffins, etc., may also be used to fill space 47. Sealing the casing requires that a second rubber gasket 4-6 be placed to fill the casing opening over the liquid before the plug 16 is inserted and held in position by the pin 17. Because of the offset mounting provided for the plug 16, the latter will be apt to twist sideways around the pin and bind in the casing in the event that the plug moves when the explosive is detonated.

At the point where it is intended that the rock bolt be anchored, a hole 50 is drilled through the strata 51. For a typical installation, the use of a one and one-half inch rock bit would be suitable to drill a hole 54), having a proper diameter to accommodate a bolt casing having a one and one-quarter inch outside diameter. The depth of this hole into strata would ordinarily be suflicient when all of the bolt casing may be received within this hole beyond the surface broken material. Rubber rings 48 and 49, fitted upon the casing 10, and bolt 25), respectively, fore and aft of the rock bolt, are provided to center the bolt and casing when they are properly located within the hole 50. However, before the rock bolt is inserted, a heavy gauge anchor plate 52 is slipped over the threaded end 23, and held in place on the bolt by a nut 53 screwed on the bolt end 23. The rock bolt is thereafter pushed up into hole 50, until anchor plate 52 is close to or nearly engages the outer surface of strata 51, with the wires 49 extending out from the edge of the plate. In a vertical hole the bolt will need a temporary support at the proper elevation until it is anchored to the strata. When the rock bolt is suitably in place as indicated, an electric current such as from a battery, is supplied to the extended wires 40 to operate the detonator 35, and explode the capsulated Primacord charge 39.

ties for the rock bolt.

A shock wave radiating out from the ensuing explosion is received by the water in the space 47, and efficiently expended on the casing 10, to cause it to expand against the inside surface of hole 50. Functioning in this manner, the invention provides a water coupling between the points of explosion and the casing wall, which is effective to dampen the explosive shock. As a result, the shock wave accomplishes the expansion anchoring of the rock bolt, without fracturing its casing 10.

Some important advantages of the rock bolt according to the invention, are made evident by reference to FIGS. 2a and 2b, illustrating rock bolts anchored in strata. In the exemplary showing of FIG. 2a, the rock bolt comprises a one-inch bolt 20, and a casing 10 which was originally a one and one-quarter inch diameter cylinder. An explosive charge three and one-half inches long was provided to effectuate the expansion of the casing. It was found that the expanded area for contacting the strata, produced by the explosion of this charge was approximately 11 square inches. The outer surface area of the expanded casing is effectively shaped by the surface of the drilled hole 50, to have a gripping conformation in that the expanded casing intimately fills all of the surface irregularities of the hole. In effect, it is the constant compressive force of the expanded casing which accomplishes the anchorage of the rock bolt. Consequently, an increased expanded area of casing for contacting the strata of the hole, results in additional anchoring capibili- Shown in FIG. 2b, is a rock bolt identical to that found in FIG. 2a, except that it was equipped with an explosive charge ten and one-half inches long. As a result, the area wherein the expanded casing 10 contacted the hole 50, was approximately 33 square inches. The competency of the ground in which the rock bolt is to be secured, to a large extent determines the length of explosive charge to be used in a particular rock bolt. Anylength necessary to obtain satisfactory anchorage up to practically the full length of the hole, may be used, as might be the case for anchoring the rock bolt in soft ground.

A still further improvement in the anchoring capabilities which may be provided for rock bolts according to the invention, is made evident in the simplified showing of FIGS. 3a and 3b wherein detailed structural parts are omitted. The representation of FIG. 3a, includes a specific arrangement for the explosive charge wherein the cuts of Primacord 61, are of l75-grain material, and the cuts 62 are of IOU-grain material. Detonation of this arrangement by the detonator 35, produces alternate areas of two degrees of expansion along the casing 10, as indicated in FIG. 3a, by the dotted line contour 64. This rippled conformation for the contacting area was found to be particularly advantageous where the ground receiving the rock bolt was soft or of a spongy consistency. It is obvious that numerous variations of this form of the invention are possible, one of which is shown in FIG. 3b. In this figure, the cuts of Primacord 65 are of grain material, the cuts 66 are of grain material, and the cuts 67 are of -grain material. Detonation of this arrangement of charges produces conical wedges formed by the alternate areas of three degrees of expansion along the casing 10, indicated by the dotted line contour 68.

While preferred embodiments of the invention has been illustrated and described herein, it is to be understood that the invention is not limited thereby, but is susceptible of changes in form and detail.

What is claimed is:

1. A rock bolt comprising a threaded rod and an anchoring means for securing the bolt in an opening through stratified ground, said anchoring means comprising an elongated hollow casing having individual openings at its opposite ends, means attaching said casing to the rod, means in said casing sealing the said openings therein comprising individual gasket elements disposed contiguous to an end surface of said rod within one end opening of said casing, and adjacent the other end opening of said casing, respectively, an elongated hollow container extending within said casing along approximately the length between its opposite ends and supported within the casing and out of contact therewith to provide a space between the container and casing, one end of said container being in contact with said contiguous gasket element, explosive means selectively arranged in said container, a substantially incompressible, fluid mass filling said space, and a means attached to said container to detonate the explosive means whereby a shock wave produced by said explosion is transmitted through said fluid mass to expand the hollow casing into contact with the stratified ground.

2. The rock bolt of claim comprises a liquid.

3. The rock bolt of claim comprises a gel.

4. The rock bolt of claim comprises a wax.

5. The rock bolt of claim comprises a fat.

6. A rock bolt comprising a threaded rod and an anchoring means for holding fast the bolt in an opening through stratified ground, said anchoring means comprising a first hollow enclosure having open ends, means fixing a portion of said rod in one of said open ends, means in said casing for sealing said open ends comprising separate gasket elements disposed contiguous to a surface of said rod within said one open end of the casing, and adjacent the other of said open ends, respectively, a second hollow enclosure supported within the first whereby said second hollow enclosure is in contact with said contiguous gasket and out of contact with the first hollow enclosure to provide a space between the two enclosures, explosive means selectively arranged in said second enclosure and a liquid filling the said space, and a means attached to said second enclosure to detonate the explosive means whereby a shock wave produced by said explosion is transmitted through the liquid to expand the first enclosure into contact with the stratified ground.

7. A rock bolt comprising a threaded bolt element and anchoring means securing the rock bolt in an opening through stratified ground, said anchoring means comprising a hollow cylindrical casing open at opposite ends, a portion of said bolt element being fixed in the opening of one of said opposite ends, means including gaskets sealing said open opposite ends, a hollow cylindrical container whose length is approximately the same as that of the casing, and means fastened on said container and supported within said casing to maintain the container out of contact with the casing to define a space therebetween, and in contact with one of said sealing gaskets, explosive means arranged in said container, and a liquid filling the said space, and a means attached to said container to detonate the explosive means whereby a shock wave produced by the explosion is transmitted through the liquid to expand the hollow casing into contact with the stratified ground.

1 wherein the fluid mass 1 wherein the fluid mass 1 wherein the fluid mass 1 wherein the fluid mass 8. A rock bolt comprising a threaded rod and anchoring means securing said bolt in an opening in stratified ground, said anchoring means comprising an elongated hollow enclosure having first and second open ends, means fastening a portion of said rod in said first open end, means sealing said open ends including gasket elements and a plug supported in said second open end for rotative displacement, an elongated capsule, and means supporting the capsule within the enclosure to maintain the said capsule out of contact with the enclosure to define a space therebetween, and contiguous to said gasket elements, explosive means arranged in said capsule, and a liquid filling the said space, and a means attached to said capsule adjacent to one of said gasket elements to detonate the explosive means whereby a shock Wave produced by said explosion is transmitted through the liquid to expand the hollow enclosure into contact with the stratified ground.

9. A rock bolt comprising a threaded rod and an anchoring means for securing the bolt in an opening in stratified ground, said anchoring means comprising an elongated enclosure fixed to the rod at one end thereof, an elongated capsule element whose length is approximately equal to that of the enclosure supported by means within the enclosure to provide a space between elongated surfaces of the capsule and enclosure, explosive means arranged in said capsule in an end to end line of cut sections of explosive materials, the relative amount of such materials varying from one section to the next, a liquid filling the said space, and means in contact with said capsule and the explosive means therein to detonate the explosive means whereby a shock wave produced by said explosion is transmitted through the liquid to expand the enclosure into contact with the stratified ground.

10. The rock bolt of claim 9, wherein a series of varia tions in the relative amounts of explosive materials in the section to section arrangement of cut sections of explosive materials, is repeated a plurality of times in the capsule.

References Cited in the file of this patent UNITED STATES PATENTS 2,214,226 English Sept. 10, 1940 2,269,646 Burke Jan. 13, 1942 2,570,003 Palmer Oct. 2, 1951 2,618,192 Temple Nov. 18, 1952 2,661,649 Skinner Dec. 8, 1953 2,779,279 Maiwurm Jan. 29, 1957 2,903,504 Tuck Sept. 8, 1959 2,978,796 Kemeny Apr. 11, 1961 3,036,373 Drexelius May 29, 1962 3,045,339 Callahan July 24, 1962 OTHER REFERENCES Pp. 89-96 of Materials in Design Engineering, July 1960, vol. 52, No. 1, pub. by Reinhold Pub. Corp., 430 Park Ave., New York 22, NY. 

1. A ROCK BOLT COMPRISING A THREADED ROD AND AN ANCHORING MEANS FOR SECURING THE BOLT IN AN OPENING THROUGH STRATIFIED GROUND, SAID ANCHORING MEANS COMPRISING AN ELONGATED HOLLOW CASING HAVING INDIVIDUAL OPENINGS AT ITS OPPOSITE ENDS, MEANS ATTACHING SAID CASING TO THE ROD, MEANS IN SAID CASING SEALING THE SAID OPENINGS THEREIN COMPRISING INDIVIDUAL GASKET ELEMENTS DISPOSED CONTIGUOUS TO AN END SURFACE OF SAID ROD WITHIN ONE END OPENING OF SAID CASING, AND ADJACENT THE OTHER END OPENING OF SAID CASING, RESPECTIVELY, AN ELONGATED HOLLOW CONTAINER EXTENDING WITHIN SAID CASING ALONG APPROXIAMATELY THE LENGTH BETWEEN ITS OPPOSITE ENDS AND SUPPORTED WITHIN THE CASING AND OUT OF CONTACT THEREWITH TO PROVIDE A SPACE BETWEEN THE CONTAINER AND CASING, ONE END OF SAID CONTAINER BEING IN CONTACT WITH SAID CONTIGUOUS GASKET ELEMENT, EXPLOSIVE MEANS SELECTIVELY ARRANGED IN SAID CONTAINER, A SUBSTANTIALLY INCOMPRESSIBLE, FLUID MASS FILLING SAID SPACE, AND A MEANS ATTACHED TO SAID CONTAINER TO DETONATE THE EXPLOSIVE MEANS WHEREBY A SHOCK WAVE PRODUCED BY SAID EXPLOSION IS TRANSMITTED THROUGH SAID FLUID MASS TO EXPAND THE HOLLOW CASING INTO CONTACT WITH THE STRATIFIED GROUND. 